Xander said it in Inca Mummy Princess at the beginning when they were in the museum about Ronnie Munson who was scrapping at a statue. he said "What he lacks in smarts, he makes up for in lack of smarts" and Willow replies "you're just bitter because of that time he beat you up every day for 7 years" and Xander looked at her and went "...yeah, I'm irrational like that"

Xander said it in Inca Mummy Princess at the beginning when they were in the museum about Ronnie Munson who was scrapping at a statue. he said "What he lacks in smarts, he makes up for in lack of smarts" and Willow replies "you're just bitter because of that time he beat you up every day for 7 years" and Xander looked at her and went "...yeah, I'm irrational like that"